Large loads are applied in the radial direction during operation to the rotational support section of various kinds of power mechanisms in a vehicle such as an automobile or train. Therefore, conventionally, radial bearings 1, such as illustrated in FIG. 24, that have excellent load performance for loads in the radial direction have been widely used as the bearings in this kind of rotational support section.
A radial roller bearing 1 is constructed such that a plurality of rollers (including needle rollers) are held between a cylindrical shaped outer-ring raceway 3, which is formed around the inner circumferential surface of an outer-diameter side member 2 such as a housing that does not rotate during operation, and a cylindrical shaped inner-ring raceway 5, which is formed around the outer circumferential surface of a shaft 4 such as a rotating shaft, by a cage 7 so as to be able to roll freely. Examples of the outer-diameter side member 2 and the shaft 4 also include a combination of a gear or roller that rotates during operation and a support shaft thereof that does not rotate during operation.
The cage 7 is made into a complete cylindrical shape using a synthetic resin material. As illustrated in FIG. 25, this cage 7 has a pair of rim sections 8, which are circular ring shaped and that are arranged concentric with each other, having a space between them in the axial direction, and a plurality of column sections 9, which intermittently located in the circumferential direction and span between the rim sections 8. The portions that are surrounded on four sides by adjacent column sections in the circumferential direction and the rim sections 8 on both sides function as pockets 10 for holding the rollers 6 so as to be able to roll freely. The cage 7 holds the rollers 6 inside the pockets 10 so as to be able to rotate freely, and with a plurality of rollers 6 arranged in the circumferential direction with a specified interval between them (for example a uniform interval), the cage 7 is arranged between the inner circumferential surface of the outer-diameter side member 2 and the outer circumferential surface of the shaft 4 so as to be able to freely rotate relative to the outer-diameter member 2 and the shaft 4. The cage 7 rotates relative to the outer-diameter side member 2 and shaft 4 due to the revolving motion of the rollers 6.
Axial draw molding, which is one method for forming this kind of cage, is performed by performing injection molding of synthetic resin into the cavity of a mold (axial draw mold) that is composed of a pair of split molds (mold elements), after which these split molds are pulled apart in the axial direction. Therefore, when removing the split molds, the split molds are pulled apart such that stopper sections (portions that correspond to engagement allowance), which are provided so as to hang over the edge sections of the opening of the pockets and are for preventing the rollers from falling out, are not damaged by plastically deforming or whitening. Therefore, axial draw molding is used when it is necessary to increase the volume of the stopper sections due to an increase in the roller diameter or increase in the number of rollers, and the work of elastically pressing and expanding the stopper sections and removing the mold elements from the outer-diameter side becomes difficult, and when removing the mold elements to the outside in the radial direction by arranging the column sections further outward in the radial direction than the pitch circle diameter of the rollers. For example, when using radial draw molding, which uses metal mold elements that move in the radial direction, when making a cage having construction in which the volume of the stopper sections is large, curling back of the stopper sections becomes large, and the stopper sections are not able to sufficiently prevent the rollers from coming out. On the other hand, with axial draw molding, the mold elements can be removed without curling back the stopper sections, so the stopper elements can sufficiently prevent the rollers from coming out.
Incidentally, when assembling the radial roller bearing 1, in order to place the cage 7 around the inner-ring raceway 5, the cage 7 may need to be inserted from the end section of the shaft 4, and further moved in the axial direction until it surrounds the inner-ring raceway 5. However, when there is an obstacle such as a flange shaped protrusion whose outer diameter dimension is larger than the inner diameter dimension of the cage 7 located in a portion of the outer circumferential surface of the shaft 4 in the axial direction between the end section of the shaft 4 and the inner-ring raceway 5, that obstacle will be in the way, and it is not possible to move the cage in the axial direction to where it will surround the inner-ring raceway 5.
Therefore, as a cage that is able to eliminate this kind of problem, a cage (split cage) is disclosed in JP 2-089814 (A) and GB 1,352,909 (A) that is made using axial draw molding so as to have non-continuous section in one location in the circumferential direction. FIG. 26 illustrates the cage 7a that is disclosed in GB 1,352,909 (A). The cage 7a is made using synthetic resin, and cuts 18a, 18b are provided in portions of the pair of rim sections 8a, 8b where the phase in the circumferential direction is nearly the same as each other. As a result, a non-continuous section 11 is formed at one location in the circumferential direction of the cage 7a. End sections 12a, 12b of the cage 7a that are composed of the rim sections 8a, 8b and column sections 9 and that are provided on both sides of the non-continuous section 11 fit together with an uneven fit by way of a fitting section 13 such that relative displacement in the axial direction and radial direction is not possible.
A set each of outer-diameter side fitting pieces 14a, 14b and inner-diameter side fitting pieces 15a, 15b that make up the fitting section 13 are formed on the end sections 12a, 12b. More specifically, on one end section 12a, an outer-diameter side fitting piece 14a is formed on one half section in the axial direction of the outer-diameter side half section, and an inner-diameter side fitting piece 15a is formed on the other half section in the axial direction of the inner-diameter side half section. Moreover, on the other end section 12b, an outer-diameter side fitting piece 14b is formed on the other half section in the axial direction of the outer-diameter side half section, and an inner-diameter side fitting piece 15b is formed on the one half section in the axial direction of the inner-diameter side half section. In the outer-diameter side half section and inner-diameter side half section of the fitting section 13, the pair of outer-diameter side fitting pieces 14a, 14b and pair of inner-diameter side fitting pieces 15a, 15b fit together in the axial direction. Moreover, in the one half section in the axial direction and the other half section in the axial direction of the fitting section 13, the outer-diameter side fitting piece 14a and the inner-diameter side fitting piece 15b, and the outer-diameter side fitting piece 14b and the inner-diameter side fitting piece 15a fit together in the radial direction. The example in the figure illustrates the state in which the end sections 12a, 12b are not fitted together, however, when the cage 7a is assembled in the radial roller bearing, the width of the non-continuous section 11 is narrowed and the end sections 12a, 12b fit together.
Moreover, outer-diameter side concave sections 16a and inner-diameter side concave sections 16b are formed on the circumferential surfaces of the pair of rim sections 8a, 8b. More specifically, on the outer circumferential surface of one rim section 8a, outer-diameter side concave sections 16a that are recessed inward in the radial direction are formed in the portions that are aligned in the axial direction with the pockets 10, and on the inner circumferential surface of the other rim section 8b, inner-diameter side concave sections 16b that are recessed outward in the radial direction are formed in the portions that are aligned in the axial direction with the pockets 10.
The cage 7a, having construction such as described above, is formed using axial draw molding. Therefore, when compared with a cage that is made using radial draw molding in which the mold is composed of a pair of mold elements that move in the axial direction and a plurality of mold elements that move in the radial direction, and thus the shape thereof is complex, it is possible to keep the manufacturing cost low. Furthermore, by elastically deforming the cage 7a, it is possible to expand the width of the non-continuous section 11 in the circumferential direction. Therefore, by expanding the width of this non-continuous section so as to be larger than the dimension of the outer diameter of the shaft 4, such as the rotating shaft, with which the cage 7a is assembled, the non-continuous section 11 can pass over the shaft 4, and the cage 7a can be assembled around the shaft 4. Alternatively, by elastically expanding the inner diameter dimension of the cage 7a enough to be able to pass over an obstacle, it is also possible to assemble the cage 7a by moving the cage in the axial direction to where it is around the shaft 4.
In the case of a cage 7a having construction such as described above, the shapes of both end surfaces in the axial direction (shape of the side surfaces in the axial direction of the pair of rim sections 8a, 8b) are different on one end side and the other end side. More specifically, the rim section 8a on one end side is such that outer-diameter side concave sections 16a are formed on the outer circumferential surface, so the side surface on the outer diameter side thereof becomes a non-continuous surface, and the outer-diameter dimension thereof is larger in the portions that are aligned in the axial direction with the column sections 9 than in the portions that are aligned in the axial direction with the pockets, however the side surface on the inner-diameter side of the rim section 8a on one end side is a continuous surface, and the inner-diameter dimension thereof is fixed. On the other hand, the rim section 8b on the other end side is such that inner-diameter side concave sections 16b are formed on the inner circumferential surface, so the side surface on the outer-diameter side is a continuous surface, and the outer-diameter dimension thereof is fixed, however, the side surface on the inner-diameter side of the rim section 8b on the other end side is a non-continuous surface, and the inner-diameter dimension in portions that are aligned in the axial direction with the columns 9 is less than in portions that are aligned in the axial direction with the pockets 10.
Even when using the cage 7a in which the shapes of the end surface on both ends in the axial direction are different in this way, as long as the guide surface that is provided on the opposing members such as the rotating shaft around which the radial roller bearing is assembled has construction that is able to support the entire area of the end surfaces in the axial direction of the cage 7a (the entire range in the radial direction and circumferential direction), there is no particular problem. However, in the case of construction in which the guide surface that is provided on the opposing member is not able to support the entire area of the end surfaces in the axial direction of the cage 7a, such as in the case of lining of a DCT (dual clutch transmission), there is a possibility that the following problems will occur. In other words, on both end surfaces in the axial direction of the cage 7a, when the non-continuous sections where the area becomes small (side surface on the outer-diameter side of the rim section 8a, or side surface on the inner-diameter side of the rim section 8b) come in contact with the guide surfaces of the opposing members and thus the radial roller bearing is guided (positioned) in the axial direction, there is a possibility that the non-continuous sections and the guide surfaces will come in strong contact due to a pressure force in the axial direction caused by skewing of the rollers, which causes wear due to friction on the end surfaces (non-continuous sections) in the axial direction of the cage 7a. In order to prevent the occurrence of this kind of friction, it is possible to use a method of limiting the assembly direction of the radial roller bearing (cage 7a) (causing the continuous sections to come in contact with the guide surfaces), however, in that case, a problem occurs in that work efficiency when assembling the radial roller bearing is impaired.
Moreover, in the case of the cage 7a having construction as described above, when the dimension in the axial direction of the cage 7a is made small in order to assemble the cage 7a into a radial roller bearing having small dimensions in the axial direction (width dimension), there is a possibility that the following kind of problem will occur. In other words, the cage 7a is such that dimension in the axial direction and dimension in the radial direction of all of the fitting pieces 14a, 14b, 15a, 15b of the fitting section 13 are about half the dimension in the axial direction and dimension in the radial direction of the end sections 12a, 12b. Therefore, the area of the end surfaces in the circumferential direction of the fitting pieces 14a, 14b, 15a, 15b is about ¼ the area of the overall end surfaces 17a, 17b that face each other in the circumferential direction on both sides of the non-continuous section 11. Moreover, it becomes difficult for the size of all of the gaps that are formed between the end surfaces in the circumferential direction of the fitting pieces 14a, 14b, 15a, 15b, and opposing surfaces that face these end surfaces in the circumferential direction to match. The reason for this is that regulating the size of the gaps so that they are all the same requires very good injection molding performance and highly precise molds, which, together with being difficult from a manufacturing aspect, leads to a very large increase in manufacturing cost.
Therefore, when the end surfaces 17a, 17b come in contact (collide) in the circumferential direction during operation of the radial roller bearing in which the cage 7a is assembled, there is a possibility that only one of the end surfaces in the circumferential direction of the fitting pieces 14a, 14b, 15a, 15b and the opposing surface thereof will come in contact, and the contact surface area will be reduced. In this kind of case as well, by making the dimension in the axial direction of the cage 7a sufficiently large, it is possible to maintain the contact surface area and make it difficult for this problem to occur, however, as the dimension in the axial direction of the cage 7a become small, it become difficult to sufficiently maintain the contact surface area. Also, in a case such as this in which it is difficult to sufficiently maintain the contact surface area, when the end surfaces 17a, 17b come in contact with each other, the end surfaces 17a, 17b tilt and are not parallel with each other, so the rollers that are held near the end sections 12a, 12b become skewed. As a result, there is a possibility that the behavior of the cage 7a will become unstable. Moreover, moment loads that are applied to the cage become large, and there is a possibility that the cage 7a will elastically deform into a non-cylindrical shape, causing the behavior of the cage 7a to become unstable. Moreover, when skewing occurs, or when stress becomes concentrated in the areas of contact when the end surfaces 17a, 17b come in contact with each other, there is a possibility that the cage 7a will become damaged.
Furthermore, in the case of the cage 7a having a non-continuous section 11 in one locating in the circumferential direction as described above, there is a possibility that, due to handling error during assembly work, the width of the non-continuous section 11 will be excessively expanded in the circumferential direction. When the non-continuous section is excessively expanded in the circumferential direction in this way, there is a possibility that the cage 7a made of synthetic resin will whiten, or that the openings of the plurality of pockets will expand, and the rollers 6 that are held inside the pockets 10 will fall out.
As a cage that is able to avoid this situation, there is a cage 7b such as illustrated in FIG. 27A and disclosed in DE 4,222,175 (A1). In the case of this cage 7b, of the pair of rim sections 8c, 8d, cuts 18c, 18d are provided in portions where the phase in the circumferential direction is nearly same. Together with this, an elastic connecting section 19 is provided that spans between one end section in the circumferential direction of one rim section 8c (end section below the cut 18c in the figure) and the other end section in the circumferential direction of the other rim section 8d (end section above the cut 18d in the figure). The elastic connecting section 19 is thin compared to the rim sections 8c, 8d and the column sections 9.
This kind of elastic connecting section 19 is for allowing the inner-diameter dimensions of the cage 7b to expand elastically, and as illustrated in FIG. 27B, as the width of the cuts 18c, 18d expand in the circumferential direction, the elastic connecting section 19 elastically stretches. The amount that the elastic connecting section stretches is prevented from exceeding a limit, which prevents the width of the cuts 18c, 18d from expanding excessively. Together with this, the elastic restoration force that occurs in the elastic connecting section 19 acts to return the cuts 18c, 18d to the original width.
This kind of cage 7b can also prevent the occurrence of fretting wear in the outer-ring raceway and inner-ring raceway of the radial roller bearing. In a rotation support section in a manual transmission for an automobile such as illustrated in FIG. 28, the gears 20a, 20b of the automobile manual transmission are placed around a power transmission shaft 21 by way of radial roller bearings 1a, 1b and synchronization mechanisms 22a, 22b so as to be concentric with the power transmission shaft 21. When a transmission speed that corresponds to one of the gears 20a is selected, the gear 20a that corresponds to the selected transmission speed engages with the power transmission shaft 21 by way of a synchronization mechanism 22a, and rotates in synchronization with the power transmission shaft 21. On the other hand, the other gear 20b that does not correspond with the selected transmission speed is able to rotate relative to the power transmission shaft 21. The radial roller bearings 1a, 1b are provided to allow the relative rotation between the gear 20a or 20b that does not correspond with the selected transmission speed and the power transmission shaft 21.
Therefore, when a transmission speed that corresponds to one gear 20a is selected, the rollers 6a of the radial roller bearing 1a that is provided between the gear 20a that corresponds with the selected transmission speed and the power transmission shaft 21 do not roll and revolve (relative rotation against the gear 20a and the power transmission shaft 21) between the outer-ring raceway 3a, which is the inner circumferential surface of the gear 20a, and the inner-ring raceway 5a, which is the outer circumferential surface of the power transmission shaft 21. However, even in this state, due to vibration caused operation, or due to movement of the load zone and no-load zone as the gear 20a and power transmission shaft 21 rotates, the rollers 6a minutely displace (vibrate) in the circumferential direction of the gear 20a and power transmission shaft 21. This kind of vibration makes it easy for fretting wear to occur in the outer-ring raceway 3a and inner-ring raceway 5a. 
In this kind of case as well, in this cage 7b, the elastic connecting section 19 is elastically stretched due to centrifugal force that is caused by the rotation, and this causes the diameter of the cage 7b to expand, or as the rotational speed decreases, the elastic connecting section 19 is elastically restored, which causes the diameter of the cage 7b to contract. Therefore, it is possible to cause the area of contact between the rolling surfaces of the rollers 6a and the outer-ring raceway 3a and inner-ring raceway 5a to move (fluctuate), which makes it possible to suppress fretting wear.
However, also in the case of the cage 7b having this kind of construction, there is the possibility that the following problems will occur. In other words, with the elastic connecting section 19 spanning between one end section in the circumferential direction of one rim section 8c and the other end section in the circumferential direction of the other rim section 8d, there is only one connecting section, so depending on the operating conditions, there is a possibility that the elastic force of the elastic connecting section 19 will not be sufficient. Moreover, during operation, when expanding or contracting the diameter of the cage 7b, the elastic connecting section 19 applies a moment to the one end section in the circumferential direction of one rim section 8c and the other end section in the circumferential direction of the other rim section 8d, and these portions are pushed or pulled in opposite directions in the axial direction from each other. As a result, the side surface in the axial direction of one end section in the circumferential direction and the side surface in the axial direction of the other end section in the circumferential direction of the rim sections 8c, 8d (the side surfaces in the axial direction of the portions on both sides of the cuts 18c, 18d) are no longer on the same plane. Therefore, there is a possibility that the side surfaces in the axial direction of the rim sections 8c, 8d will become inclined with respect to the guide surfaces for guiding these side surfaces in the axial direction (virtual planes that are orthogonal to the center axis of the cage 7b).
Moreover, in the case of this cage 7b, due to having a small thickness, the strength of the elastic connecting section 19 is low compared to the other portions, so the cooling contraction of this elastic connecting section 19 is large compared to the other portion, and irregular cooling easily occurs. Therefore, there is a possibility that the distance between the portions that are connected by the elastic connecting section 19 (one end section in the circumferential direction of one rim section 8c and the other end section in the circumferential direction of the other rim section 8d) may be less than a desired value. In the initial state as well, there is a possibility that the side surfaces in the axial direction of the rim sections 8c, 8d will be inclined with respect to the guide surfaces provided on the opposing members. Furthermore, of the cage 7b, it becomes easy for the rollers that are held in the pockets that are located near both end sections on both sides of the cuts 18c, 18d to become skewed. As a result, there is a possibility that the behavior of the cage 7b will become unstable.